This invention concerns arrangements and methods for achieving a high aerodynamic efficiency of the mast and adjacent sail areas and more particularly concerns such arrangements and methods having particular application to lightweight sailing craft such as windsurfing sailing boards. The present invention also concerns arrangements compatible with the manual exertions required in maneuvering such craft, specifically the need for easy righting of the sail and mast from a capsized condition.
Windsurfing sailing boards consist of a simple board hull on which is pivotally attached a lightweight flexible mast and a boom attached intermediate the height of the mast surrounding the sail and secured along one side thereof to the mast. The sail is attached to the boom and mast so as to be drawn into a curved shape for optimal sail shape in profile, i.e., to minimize induced drag by creating a roughly elliptical sail profile.
The sailor stands atop the board hull and grasps the boom to execute sailing maneuvers by shifting of body weight and the sail angle in the manner well known to those skilled in the art.
The sail is relatively small in area and the craft is lightweight, such that aerodynamic efficiency of the mast and adjacent sail areas has a pronounced effect on craft performance. That is, the lift achieved by airflow past the mast and adjacent sail areas significantly affects performance.
Swamping of the craft is an oftentimes occurrence, such that ease in righting the mast and sail assembly are of great importance in the design of such craft.
Such craft are usually sold for relatively low prices, such that a simple, inexpensive construction is a necessary design criteria.
Common prior art arrangements for securing the sail to the mast are shown in FIGS. 1a-1d. In the first of these shown in FIG. 1a, a sleeve 1 is formed along the luff of the sail 2, sized such that it is to be tightly fit to the mast 3 which is received within the sleeve 1. Oftentimes, full-length battens are provided, received in pockets formed in the sail and, in the tight sleeve design, the orientation of the sleeve is such as to allow smooth transitioning of battens into the mast sleeve perimeter as shown.
While simple, this design exhibits poor aerodynamic efficiency due to the "dead zone" to the rear of the mast adjacent to the trailing sail surface.
In an attempt to improve the aerodynamic efficiency, so-called bag sleeves have been developed, shown in FIG. 1b, in which the bag sleeve 4 extends several inches to the rear of the mast 3. This design is effective in substantially improving the aerodynamic efficiency, although some turbulence still results, as indicated. For board sailing applications, the bag sleeve 4 has a tendency to trap water upon upsetting of the sail, making the righting maneuver more difficult.
Further improvements in aerodynamic efficiency have been produced by so-called "camber influencers", shown in FIG. 1c, which are wishbone-shaped plastic devices 5 shaped like a capital letter "A", with the legs of the "A" fit against the mast end and the peak of the "A" being slotted to receive the battens. These devices have been effective in substantially improving the aerodynamic efficiency of the bag sleeve 4, while providing a more rigid definition of the transition from the mast 3 to the main sail area 2.
The most highly efficient aerodynamic shape has been the so-called "wing mast", shown in FIG. 1d, in which the mast itself is shaped as an air foil 6 with a leading parabolic surface area 7 forward of the mast and trailing smoothcurved sides 8 converging to the rear of the mast. A central slot 9 is provided for securement of the sail 2 to the mast. While providing optimum aerodynamic efficiency, the wing mast incurs a substantial cost and weight penalty resulting from the increased structural requirements of the wing section. Importantly, the mast profile is incompatible with a full length flexible mast to allow full length curvature thereof, such that an optimal profile is only achievable by add-on fairing members.
Prior art efforts have also included the use of shaped rigid members fit over the mast and adjacent sail areas, but this approach also increases the mass and complexity of the craft and is incompatible with full length curving of a flexible mast.
It is also important that any such arrangement and method would be compatible with other standard rigging components to render application of the arrangement simpler and lower in cost.
Accordingly, it is an object of the present invention to provide an arrangement for achieving a highly efficient aerodynamic shape of the mast and adjacent sail areas.
It is another object of the present invention to provide such an arrangement which is compatible with flexible mast curved luff profile constructions, and which is compatible with standard rigging components.
It is yet another object of the present invention to provide such an arrangement which is simple, low in cost and lightweight.
It is still another object of the present invention to provide such an arrangement which allows for easy righting of the mast from a capsized condition.